Unramified degree of a local field (reviewed)

Let $K$ be a finite extension of $\Q_p$, and $K^{un}$ its unramified subfield. Then the unramified degree of $K$ is the degree $[K^{un}:\Q_p]$.

Since $\Q_p$ has a unique unramified extension of degree $n$ for each positive integer $n$, the unramified degree of an extension determines its unramified subfield.